The amount and kind of genetic variation for quantitative traits revealed by allozyme polymorphism and nucleotide diversity is reviewed. At the nucleotide level, practically every locus is polymorphic, while only 15% of polymorphisms show up at the biochemical level. The increasingly complex picture of the genetic material revealed by molecular studies is discussed. Despite the fact that it does not accommodate these complexities, the standard quantitative genetics model has been a satisfactory basis for successful breeding programmes. Developments in the last two decades which reinforce this success are the statistical developments which lead to optimal breeding value estimation, and the gene flow theory which accommodates complexities in population structure.
With the sharpening division of the world agricultural economy between developed and developing countries, the major challenge for quantitative genetics and animal breeding in the decades ahead is clearly in the latter group. Additional challenges are presented by the need to exploit new molecular and reproductive technologies, and by unresolved questions concerning the effects of heterozygosity, epistasis and non-nuclear inheritance.

E. P Cunningham

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XIII. Plenary lectures, molecular genetics and mapping, selection, prediction and estimation., , 4–14, 1990
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